1. Field of the Invention
The present invention relates to a disc erasing apparatus and more particularly, to an apparatus for erasing a record of each track in a disc such as a magnetic disc used in an electronic still camera in which a plurality of tracks are formed concentrically.
2. Description of the Prior Art
Recently, an electronic still camera has been developed, which is disclosed in, for example, an article by N. Kihara et al., entitled "THE ELECTRONIC STILL CAMERA A NEW CONCEPT IN PHOTOGRAPHY", IEEE Transactions on Consumer Electronics, Vol. CE-28, No. 3, Aug. 1982, pp. 325-331. Such an electronic still camera is adapted such that a plurality of tracks are formed concentrically on a magnetic disc and signals for a field or a frame of an imaged still picture are recorded on each track.
More specifically, since a magnetic disc is used in the electronic still camera as a recording medium as described above, recording, reproducing and erasing can be performed, unlike a conventional image film. It has been proposed that the electronic still camera is provided with an erasing function as well as recording and reproducing functions to, for example, selectively erase a record of each track of a recorded magnetic disc, so that editing of the record may be performed.
In order to provide the function for erasing a record of each track, a magnetic head for erasing only may be provided independently of a magnetic head for recording and reproduction. However, if such a head for erasing only is provided, the number of heads increases, so that the entire structure of the apparatus is complicated.
At the time of reproduction of the magnetic disc, tracking control is generally performed to prevent decrease in the reproduced output due to deviation of track. As one system for performing tracking control, a Dither system is disclosed in, for example, an article by T. Tanaka et al., entitled "AN ELECTRONIC STILL CAMERA SYSTEM", IEEE Transactions on Consumer Electronics, Vol. CE-32, No. 3, Aug. 1986 pp. 345-354. However, when erasing is performed utilizing the head for erasing only as described above, the reproduced signal cannot be obtained from the magnetic disc and thus tracking control of the magnetic head can not be performed. More specifically, when a track to be erased is selected, the position of the head is generally fixed to a position set by accessing the track to be erased or the like, so that erasing is performed. However, if tracking control of the magnetic head is not performed at the time of erasing as described above, the actual trace position of the magnetic head at the time of erasing cannot easily correspond to a target track to be erased due to positional deviation of track caused by a positional error of the accessed head and eccentricity of the magnetic disc, so that a record of the track cannot be surely erased.
In order to solve the problems, the following has been proposed.
First, a single magnetic head used for either one or both of recording and reproduction is also used for erasing, and the magnetic head is attached to an electro-mechanical transducer such as a bimorph piezo-electric element, so that the magnetic head is moved in a width direction of the track to be erased, that is, in a radial direction of the magnetic disc at the time of erasing, which is proposed in, for example, Japanese Patent Laying-Open Gazette No. 59406/1978. According to the just-described method, erasing is performed wider than the track to be erased without providing the head for erasing only, so that the record of the track can be surely erased.
Secondly, means for transporting the magnetic head from a track to the next track in a plurality of steps is provided, so that every time the trace position of the magnetic head is moved sequentially to the position in each step associated with the target track to be erased at the time of erasing, erasing operation is repeated, which is proposed in, for example, Japanese Patent Laying-Open Gazette No. 52404/1984. According to the just-described method, the erasing is performed wider than the track to be erased, so that the record of the track can be surely erased.
Thirdly, a tracking control signal following a distorted shape of the track due to eccentricity or the like is perfectly stored in advance in the waveform storing means, so that the trace position of the head is changed following the distorted shape of the track, which is proposed in, for example, Japanese Patent Laying-Open Gazette No. 16946/1981.
However, according to the above described first and second methods, in order to erase surely the record of the target track, the width to be erased must be set to be considerably wider than the actual track width in consideration of the above described track deviation due to a positional error of the accessed head, eccentricity or the like. In this case, a record of an adjacent track is liable to be partially erased by such erasing.
In addition, according to the above described third method, waveform storing means for storing a tracking control signal for the entire position of the track to be erased and the like must be provided, so that a structure of the apparatus is complicated. Furthermore, if tracking accuracy and storage accuracy are not very high, good tracking control cannot be performed, which presents a great difficulty at the time of manufacturing.